The viscosity and structure of solutions. Part 2.—Measurement of the B coefficient of viscosity for alkali-metal chlorides in propan-1-ol–water mixtures at 25 and 35 °C

Abstract

Measurements of the B coefficients of viscosity in the Jones–Dole equation η_r= 1 +Ac^½+Bc are reported for the alkali-metal chlorides in the propan-1-ol–water system at 25 and 35 °C; they extend to 85%(w/w) propanol for Cs⁺Cl^– to 70%(w/w) propanol for Na⁺Cl^– and K⁺Cl^– and 30%(w/w) propanol for Li⁺Cl^–. Photoelectric timing and high-precision density measurements were used in determining the relative viscosities, η_r, of the solutions. Conductivity measurements of intermediate precision gave values of the limiting equivalent conductivities of the electrolytes for use in the calculation of A, above. To 50% alcohol, the equivalent conductances of the ions could be established accurately using transport numbers from another investigation. To 30% alcohol the Jones–Dole equation was obeyed by all the electrolytes except Li⁺Cl^–, where an additional term Dc², with small positive values of D, was required. For mixtures containing 50%(w/w) alcohol or more, the Jones–Dole equation was of the correct form to represent the η_r, but the values of A required were larger than the theoretical ones; the conductivity measurements indicated that the electrolytes were associated in these mixtures. The values of the ion-pair dissociation constants, determined from the conductivity measurements, were about those expected from Bjerrum theory; they were used to calculate the degree of dissociation α of the ion pairs. Values of B_i, referring to the free ions, were obtained by fitting the η_r to the equation η_r= 1 +A(αc)^½+B_iαc+B_p(1 –α)c in which B_p is the corresponding coefficient for the ion pairs. Values of the partial molal volumes of the electrolytes at infinite dilution in the various solvent mixtures were obtained from the density measurements. The densities and viscosities of the mixtures are recorded.